richard e. hughes lecture 1; p.1 from quarks to the cosmos! prof. richard e. hughes 3046 physics...

Lecture 1; p.1Richard E. Hughes

From Quarks to the Cosmos! Prof. Richard E. Hughes

3046 Physics Research Building, 614-688-5690 Email: [email protected] Course Web Address:

http://www.physics.ohio-state.edu/~hughes/freshman_seminar/

Course goals: Particle physics and astronomy have seen incredible gains over

the past twenty years. And yet, though particle physics concerns the very smallastronomy concerns the extremely large, it is clear that these two disciplines are very closely related.

This course will introduce the non-expert to these most exciting sciences, and describe the major research aims of each.

We will focus on important questions at the intersection of physics and astronomy that have some hope of being answered over the next decade.


Course Structure

Class meets once per week Each class will focus on one major research area in

particle physics/particle astrophysics Many of these but not all have some participation by OSU

physicists

Each class will be organized like a “Press Conference” Except this one! YOU are the press: After each class, writeup a ~two paragraph summary of the press

conferenceLike you might expect to see in your local paperThis should be easy: expect it should take you about 30 minutes

outside of classPrior to / after class: explore topics on web

Today’s class: brief introduction to particle physics and the important questions physicists are trying to answer


What is particle physics?

Particle physics addresses some of the most fundamental questions that people have been pondering for centuries: What are the building blocks of matter? Why are these blocks what they are? Can

we explain their properties, such as mass? How do they interact?

In a way, particle physics is complementary to cosmology: cosmology studies the largest possible objects

(such as galaxies, with hundreds of billions of stars!), and particle physics studies the smallest possible objects imaginable.


Building Blocks of Man

…or build this!Build this…


Distance Scales Football Field 109m Person: ~1.7m Hand: ~15cm Mosquito: ~2cm Ant 5mm Human hair: 100microns Human red blood cell, bacterium:10microns HIV virus: 100nm Diameter of DNA: 2nm Width of Protein: 0.5nm Radius of Hydrogen: 25pm Size of the atomic nucleus: 10fm Size of proton: 1fm Size of quarks: <10^-18m Planck Length: 10^-35m distances below this make no sense!


What is a building block?

What is the most elementary building block of matter? First, we need to define elementary:Let us define an elementary particle as something

that has no discernable internal structure; appears “pointlike”. (At least in current

experiments…)• First, people thought that the atom was elementary:

The atom, as it was envisioned around 1900 -- a ball with electrical charges inside, bouncing around! The atom, as it was envisioned around 1900 -- a ball with electrical charges inside, bouncing around!


Rutherford Scattering Experiment

Rutherford Experiment

gold foil

Most of the atom is empty space.

Hard central core!

The alpha particle is probing the structure of the gold in the foil. This basic idea has been repeated many times over the last hundred years to further probe the structure of matter.

Like firing a cannon ball at a paper towel and having the ball bounce back


The atom has a rich structure!

Eventually, it was realized that the atom is not elementary: it consists of a positively

charged nucleus and negatively charged electrons.

The properties of outermost electrons in atoms give rise to chemistry and biochemistry, with all of its complexity!

The electron, as far as we know, is elementary!

nucleusnucleus

electronelectron

If the nucleus were as big as a baseball, then the entire atom's diameter would be greater than the length of thirty football fields!

If the nucleus were as big as a baseball, then the entire atom's diameter would be greater than the length of thirty football fields!


Is the nucleus elementary, too?

Unlike the electron, the nucleus is not structureless! It consists of protons and neutrons.

But protons and neutrons are not elementary, either!

They consist of quarks, which to the best of our knowledge are elementary.

nucleusnucleus

neutronneutron protonproton

Experiment in 1960’s

High Energy Electrons


Break down H20

H HO

ep

ep enp 888

p pp n8u

d

u28 d26 e10


Break down Pb

p n82

u289 d332 e82

Pb

e125 82


H20 vs Pb

u289 d332 e82

u28 d26 e10

Pb

OH 2

The sizes of the piles are different, but ratio of u/d is not all that different and e/u ratio is not all that different. Looking at H2O and Pb this way…they don’t look all that different.


The Standard Model The most comprehensive theory developed so far that explains

what the matter is made out of and what holds it together is called the Standard Model.

In the Standard Model, the elementary particles are:

Why do quarks and leptons come in sets (which are called generations)? Why are there three of them? We don't know.

Note that the Standard Model is still a model because it's really only a theory with predictions that need to be tested by experiment! Going to very high energies the theory begins to breakdown. (Effective Theory)

6 quarks (which come in three sets)

6 leptons (which also come in three sets)

6 quarks (which come in three sets)

6 leptons (which also come in three sets)


How many quarks? Quarks: They are fundamental particles…make up

protons and neutrons…but other exotic forms of matter as well. First proposed in 1960’s.

There are 6 quarks, and they come in pairs:There are 6 quarks, and they come in pairs:

upup

downdown

charmcharm

strangestrange

top/truthtop/truth

beauty/bottombeauty/bottom

1974

1978

1995


What about the electron?

We said earlier that apart from the six quarks, the electron was also elementary.

It turns out that the electron is not alone -- it belongs to a group of six particles called leptons! Just like quarks, leptons come in pairs:

Electron neutrinoElectron neutrino

electronelectron

Muon neutrinoMuon neutrino

muonmuon

Tau neutrinoTau neutrino

tautau

e

(mass = 205 x mass of e)

(mass = 3503 x mass of e)

e


What are neutrinos? W. Pauli postulated their existence in order to save the energy

conservation principle in certain types of radioactive decays, known as beta-decays:

E. Fermi called them "neutrinos" -- "little neutrons" in Italian.

Neutrinos hardly interact with anything at all. In fact, the earth receives more than 40 billion neutrinos per second per cm2. Most of them just pass through the earth, as if it's not even there!

epnneutron decays into proton plus electron plus neutrinoneutron decays into proton plus electron plus neutrino


What particles are important? Everything you can look atcontains the simple protons neutrons, and electrons.

Everything you can look atcontains the simple protons neutrons, and electrons.

So the natural expectation is that protons, neutrons, and electrons are the most common particles in the universe. But you would be very wrong! There are about: 0.5 protons per cubic meter of universe 330 million neutrinos per cubic meter One billion photons per cubic meter


Antimatter! The quarks and leptons discussed so far make up “ordinary”

matter. For every one of these there is an antimatter counterpart.

Antiup quark, Antidown quark, etc. antielectron (positron), antielectron neutrino, etc.

Antihydrogen:

p

u

d

e

Never shake hands with your antiself!

Matter Antimatter

An oddity: as far as we can tell, all of the luminous material we see in the An oddity: as far as we can tell, all of the luminous material we see in the universe is MATTER not ANTI-MATTER!universe is MATTER not ANTI-MATTER!

The predominance of matter over antimatter in the Universe is one of the The predominance of matter over antimatter in the Universe is one of the biggest mysteries of modern high energy physics and cosmology!biggest mysteries of modern high energy physics and cosmology!


What holds everything together?

Things are not falling apart because fundamental particles interact with each other.

An interaction is an exchange of something.

? But what is it that particles exchange? There is no choice -- it has to be some other special type of particles! They are called force particles (Intermediate Vector Bosons).

A rough analogy of an interaction:the two tennis players exchange a ballA rough analogy of an interaction:the two tennis players exchange a ball


Four fundamental interactions

There are four fundamental interactions between particles:

InteractionInteraction Mediating particleMediating particle Who feels this forceWho feels this force

Strong Gluon (g) Quarks and gluons

Electromagnetic Photon () Everything electrically charged

Weak W and Z Quarks, leptons, photons, W, Z

Gravity Graviton (?) Everything!


The strong interaction The strong force holds together

quarks in neutrons and protons.

It's so strong, it's as if the quarks are super-glued to each other! So the mediating particles are called gluons.

This force is unusual in that it becomes stronger as you try to pull quarks apart. Eventually, new quark pairs are

produced, but no single quarks. That's called quark confinement.

QUARK


The electromagnetic interaction The residual electromagnetic interaction

is what's holding atoms together in molecules.

The mediating particle of the electromagnetic interaction is the photon. Visible light, x-rays, radio waves are all

examples of photon fields of different energies.

opposite charges attract

opposite charges attract


The weak interaction Weak interactions are indeed

weak: Neutrinos can only interact

with matter via weak interactions -- and so they can go through a light year of lead without experiencing one interaction!

Weak interactions are also responsible for the decay of the heavier quarks and leptons.

So the Universe appears to be made out of the lightest quarks (u and d), the least-massive charged lepton (electron), and neutrinos.

1 light year

1 light year


Gravity

The Standard Model does not include gravity because no one knows how to do it.

That's ok because the effects of gravity are tiny comparing to those from strong, electomagnetic, and weak interactions.

People have speculated that the mediating particle of gravitational interactions is the graviton -- but it has not yet been observed.


Seething Underworld

Lots of gluons, photons, even strange and charm quarks inside protons and neutrons.

e

n

p

e

e

d

d

du

u

u

g

gg

g

cc


The Big Questions

How was matter formed at the beginning of the universe?

How does it stay together? What are the fundamental building blocks of nature? What are the basic laws upon which the universe

operates? Astrophysicists have found that less than 5 percent of

the mass of the entire universe consists of the kind of "luminous" matter that we can see. What is the dark matter that makes up the rest of the universe?

Why is our universe is made of matter, while antimatter has all but disappeared?


Fermi National Accelerator LaboratoryProton-antiproton collider: Question: What are the fundamental building

blocks of nature? Only place in the world where top quarks can be made


Gamma-ray Large Area Space Telescope

Gamma Ray Bursts: Power at maximum up to 1,000,000,000,000,000,000 (quintillion) times the Sun's power

Compton Observatory all sky gamma-ray image of the unidentified sources (active galactic nuclei, pulsars, supernova remnants, dense molecular clouds, and stellar-mass black holes within our Galaxy?)

Matter that radiates across the entire electromagnetic spectrum is only 10% of the total mass of the universe: 90% of the mass of the universe does not emit light at any wavelength. Can detect this so-called dark matter by its gravitational effects on luminous matter


ATLAS

Proton-proton collider increase energy by factor of 7 over Fermi Tevatron!

Main purpose: Search for a special particle – - the Higgs – that gives all other particles MASS!


NUMI/MINOS

Idea: make neutrinoes, shoot them underground approximately 450 miles to Minnesota; study neutrino mass


Supernova / Acceleration Probe

Studying the Dark Energy of the Universe

A star's distance can be estimated from its brightness as seen on Earth, if its total emitted light is known — the farther away it is, the dimmer it appears. Accurate estimates of total emitted light are possible for only a few kinds of astronomical objects such as type Ia supernovae

most distant supernovae are dimmer than they would be if the universe were slowing under the influence of gravity; they must be located farther away than would be expected – the conclusion is: the Universe is expanding!

some form of dark energy does indeed appear to dominate the total mass-energy content of the Universe, and its weird repulsive gravity is pulling the Universe apart

richard e. hughes lecture 1; p.1 from quarks to the cosmos! prof. richard e. hughes 3046 physics...

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